linux-kernel - Re: [PATCH v2 2/5] dax: fallback from pmd to pte on error

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Message-ID: <x497ffy7wgg.fsf@segfault.boston.devel.redhat.com>
Date:	Fri, 15 Apr 2016 10:55:43 -0400
From:	Jeff Moyer <jmoyer@...hat.com>
To:	Vishal Verma <vishal.l.verma@...el.com>
Cc:	linux-nvdimm@...1.01.org, Jens Axboe <axboe@...com>,
	Jan Kara <jack@...e.cz>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Christoph Hellwig <hch@...radead.org>,
	Dave Chinner <david@...morbit.com>,
	linux-kernel@...r.kernel.org, xfs@....sgi.com,
	linux-block@...r.kernel.org, linux-mm@...ck.org,
	Matthew Wilcox <matthew.r.wilcox@...el.com>,
	linux-fsdevel@...r.kernel.org, linux-ext4@...r.kernel.org,
	Al Viro <viro@...iv.linux.org.uk>
Subject: Re: [PATCH v2 2/5] dax: fallback from pmd to pte on error

Vishal Verma <vishal.l.verma@...el.com> writes:

> From: Dan Williams <dan.j.williams@...el.com>
>
> In preparation for consulting a badblocks list in pmem_direct_access(),
> teach dax_pmd_fault() to fallback rather than fail immediately upon
> encountering an error.  The thought being that reducing the span of the
> dax request may avoid the error region.
>
> Signed-off-by: Dan Williams <dan.j.williams@...el.com>

Reviewed-by: Jeff Moyer <jmoyer@...hat.com>

> ---
>  fs/dax.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/fs/dax.c b/fs/dax.c
> index 90322eb..ec6417b 100644
> --- a/fs/dax.c
> +++ b/fs/dax.c
> @@ -945,8 +945,8 @@ int __dax_pmd_fault(struct vm_area_struct *vma, unsigned long address,
>  		long length = dax_map_atomic(bdev, &dax);
>  
>  		if (length < 0) {
> -			result = VM_FAULT_SIGBUS;
> -			goto out;
> +			dax_pmd_dbg(&bh, address, "dax-error fallback");
> +			goto fallback;
>  		}
>  		if (length < PMD_SIZE) {
>  			dax_pmd_dbg(&bh, address, "dax-length too small");